373
FXUS63 KMQT 132340
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
740 PM EDT Sat Jul 13 2024

.KEY MESSAGES...

- Seasonably warm this afternoon with a 20-30% chance of
  showers/thunderstorms over the west.

- 40-60% chance of showers and thunderstorms this evening into
  overnight hours. Marginal risk (category 1 out of 5) of severe
  thunderstorms for most of the UP. Slight risk (category 2 out
  of 5) for the far west. Main threats are large hail and
  damaging winds.

- Chances (20-40%) for thunderstorms along lake breeze
  boundaries Sunday.

- Marginal risk (category 1 out of 5) of severe thunderstorms
  Monday.

- Cooling and drying trend into the midweek portion of next
  week with the arrival of high pressure.

&&

.UPDATE...
Issued at 739 PM EDT Sat Jul 13 2024

Ongoing showers and severe thunderstorms in central Wisconsin should
continue pressing southeast through the evening. Some
sprinkles/light rain may fall in and around Menominee, but
otherwise, mostly dry conditions are now expected for the next few
hours. Current satellite analysis shows what appears to be a stable
strato layer of clouds over western Upper Michigan, implying a more
stable atmosphere. East of this area, a north south boundary is
apparent on radar through Marquette County. This boundary may be the
focus for some late evening convection, but this is very uncertain.
East of the boundary, SPC Mesoanalysis shows very little
instability, and without any real shear to speak of, I`m skeptical
about any organized development. With this being said, the HRRR,
which has been the most consistent hourly CAM this afternoon/evening
so far, is insistent on scattered showers and storms developing
around 4-7z along and just east of this boundary. Will continue to
maintain low POPs elsewhere in the western Upper Michigan given the
continued uncertainty in this forecast.

Upstream in northwest Minnesota, some convection has been observed.
If upscale development continues as the HRRR implies, development
would congeal into a bowing segment as it tracks southeast into
western WI after midnight eastern time. If this development occurs
as stated, main risk area for strong thunderstorms would be in areas
bordering the Michigan/Wisconsin stateline. However, timing suggests
even strong storms may be hard to realize.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 1235 PM EDT Sat Jul 13 2024

Upper air consists of an anticyclone centered around the Four
Corners and a cutoff low over northern SK/MB. Belt of seasonably
fast zonal flow between these two features is diffluent over the
local area. Several small areas of convection are noted in this
diffluent zone - one in far SW ON, one in northern MN, and one in
northern WI. These are being fed by modest SW winds at 850 mb and
are located in an area of steep midlevel lapse rates. These lapse
rates weaken with eastward extent, and as a result, there is
uncertainty whether the lead convective cluster over northern WI
will make it into the western UP this afternoon. This cluster has
outperformed CAM depictions of it so far, leading to greater than
normal uncertainty in its evolution. Have expanded 20-40% PoPs over
the far west for mid-afternoon to account for this. Severe risk
appears low given paltry bulk shear if storms do indeed unfold this
afternoon. Otherwise, a few showers are firing up along the lake
breeze in northeast Alger/northern Luce County. Isolated ts possible
here this afternoon.

Similar low predictability exists in the overnight hours with any
MCS activity due to wide variance in CAM output and tendency for
better instability to be located SW of the local area. As a result,
early afternoon forecast update went with a more broad-brush
approach to PoPs in the 50-60% range for the overnight hours. Severe
risk (large hail/damaging winds) does still exist mainly for the
western half of the UP if an outflow-dominant MCS does develop given
respectable convective parameters (1000-2500 J/kg MUCAPE), although
deep shear is a bit lacking at less than 30 kt.

Otherwise, the other concern is the heat with temps on track to
reach the mid-80s to near 90 (warmest in downslope zones near Lake
Superior), although dewpoints should mix out a bit in the warmest
areas with humidity contribution to apparent temps negligible.

&&

.LONG TERM /SUNDAY THROUGH SATURDAY/...
Issued at 353 PM EDT Sat Jul 13 2024

Aloft, the path of most prominent troughs and ridges is well to the
north over Canada, leaving the Upper Great Lakes in a primarily
zonal pattern through this weekend. This will lead to the primary
driver of sensible weather to be weak shortwave impulses in the
zonal flow. While the synoptic forcing may be weak and ambiguous,
hot and muggy conditions this weekend will allow for instability to
grow, allowing for the potential for strong to severe thunderstorms
over the weekend and to begin next week, especially in the form of
MCS`s. High pressure then settles over the region by Tuesday,
allowing for a cooler dry period towards the middle and late week
period next week.

Sunday, clearing via subsidence following lingering convection from
the day prior will allow for some clearing skies. This will lead to
a pretty warm day, with highs around 80 except in the south central
where highs could approach 90, though the 00Z LREF only gives about
a 10% chance of exceeding 90. Moisture values increase as well, with
the PWATs exceeding 1.5 inches representing the 90th percentile of
climatology by GRB and APX sounding climatology. Dew points are
forecast to be approaching 70 for at least some period of time for
much of the UP, with the highest chances (30-70%) of exceeding a
muggy 70 being the south-central and the east. Monday looks to be
similarly warm, though lower chances of dew points being
oppressively high.

These hot and humid summertime conditions will be accompanied with
westerly to west-northwesterly flow at 500mb, which will allow for
some minor shortwaves to progress through the region. One of these
shortwaves looks to pass just south of the MI/WI state line on
Sunday. While mesoscale ridging will act to keep larger-scale
thunderstorms away from the UP, the mid 60s+ dew points and 1000-
2000 J/kg of only weakly capped SBCAPE combine for a
climatologically favorable setup for convection over the UP. With
the southwesterly surface flow contrasting the west-northwest flow
aloft, directional shear will be present, though speed shear will be
somewhat lacking. Regardless, shear will be present enough to help
maintain whatever thunderstorms do initiate, so if enough lake-
breeze convergence zones can lift parcels enough to realize the
instability, severe weather is still a possibility for Sunday
primarily along the lake breeze in the east. Monday, another
shortwave passes from west to east across the UP starting in the
west in the early morning hours and progressing east throughout the
day. Instability does not look as strong with this wave, with the
12Z GEFS mean around 1000 J/kg, but forcing is much better, so
thunderstorms are expected with a few being potentially strong to
severe, consistent with the SPC Marginal Risk (category 1 of 5).

By Tuesday, broad troughing aloft shifts from northern Ontario
towards the East Coast and ridging fills in behind. As a result of
the advancing ridging, high pressure to around 1020mb will keep
weather quiet through at least the end of the week. A cooling trend
is also expected to accompany the arriving ridging as north and
northwest flow will bring highs only in the upper 60s and low 70s
Tuesday through Thursday. Temperatures rebound in the late week
towards more seasonably summer temperatures.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 723 PM EDT Sat Jul 13 2024

Upstream convection continues to struggle as it approaches Upper
Michigan. Recent satellite imagery suggests a mostly capped
environment over western Upper Michigan, which suggests the main
concern for convective development will be late evening over central
Upper Michigan and then upstream in Minnesota. The former may
support some thunderstorms in and around KSAW while the latter would
be a concern overnight as it tracks southeast for KCMX/KIWD. This
generally matches recent HRRR runs, but it should be stated that
there is still a good bit of uncertainty in this. Outside of
convection, VFR conditions are expected.

&&

.MARINE...
Issued at 353 PM EDT Sat Jul 13 2024

Southerly winds remain below 20 kts today as the pressure gradient
stays light. South winds increase tonight over the east to near 20
kts with a 15-25% chance for gusts reaching 25 kts tonight ahead of
the next disturbance. Some strong to severe storms are possible
tonight, especially across western Lake Superior. The main threats
are damaging winds, but large hail is also possible. Another round
of storms is expected Monday into Monday night as a low pressure
system moves through the area. Patchy dense fog is also a
possibility in the wake of any precipitation. Following the
Monday/Monday night low presusure`s cold front, west winds increase
to around 20 kts across much of the lake Monday night and Tuesday.
As high pressure begins to build in mid next week, winds look to
fall back below 20 kts, remaining light through the remainder of the
forecast period.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.

&&

$$

UPDATE...JTP
SHORT TERM...Thompson
LONG TERM...GS
AVIATION...JTP
MARINE...GS